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| Illustration 1 | g00274584 |
(1) All wheel drive piston motors | |
The hydraulic oil is supplied to all wheel drive piston motor (1) by the all wheel drive piston pump that is mounted on the transmission. The direction of rotation for all wheel drive piston motor (1) is controlled by the direction of the oil flow from the all wheel drive piston pump. The all wheel drive electronic control module (ECM) controls the outlet pressure and the ECM controls the direction of oil flow from the all wheel drive piston pump.
All wheel drive piston motor (1) is a radial piston motor. All wheel drive piston motor (1) is two speed and dual displacement. At low speeds, all wheel drive piston motors (1) will operate at high torque and the large displacement. At low speeds, all wheel drive piston motor (1) will displace 1650 cc/rev (100 cu in/rev). At high speeds, all wheel drive piston motors (1) will operate at reduced torque and the small displacement. At high speeds, all wheel drive piston motor (1) will displace 660 cc/rev (40 cu in/rev). The large displacement is used for low speed and high torque. The small displacement is used for high speed and low torque. Pilot pressure is required to change the displacement of all wheel drive piston motor (1) . This pilot signal is provided by the displacement solenoid valve in the control valve. The ECM will monitor the gear selection and the ECM will change the displacement of all wheel drive piston motor (1) . In the first speed forward through the fourth speed forward, all wheel drive piston motor (1) is set at the large displacement. In the first speed reverse through the third speed reverse, all wheel drive piston motor (1) is set at the large displacement. In the fifth speed forward through the seventh speed forward, all wheel drive piston motor (1) is set at the small displacement. In the fourth speed reverse through the fifth speed reverse, all wheel drive piston motor (1) is set at the small displacement. In the eighth speed forward and the sixth speed reverse, all wheel drive piston motor (1) is in the freewheel mode.
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| Illustration 2 | g00275201 |
(2) Spindle (3) Wheel (4) Cam ring (5) Motor housing (6) Drain line (7) Reverse line (8) Motor displacement signal line (9) Forward line (10) Orifice (11) Cylinder block (12) Distribution valve | |
Orifice (10) is a case drain that allows warm hydraulic oil to flow into the all wheel drive piston motor during warm-up. Also, orifice (10) allows fresh hydraulic oil and cooled hydraulic oil to flow into the all wheel drive piston motor during operation.
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| Illustration 3 | g00275202 |
(4) Cam ring (5) Motor housing (11) Cylinder block (13) Roller (ten) (14) Piston (ten) (15) Displacement spool (16) Distribution valve internal block (20) Distribution valve external block | |
There are four lines that are connected to each all wheel drive piston motor:
- Reverse line (7) and forward line (9)
- Motor displacement signal line (8)
- Case drain line (6)
There are six major components of the all wheel drive piston motor:
- Spindle (2)
- Cam ring (4)
- Motor housing (5)
- Cylinder block (11)
- Distribution valve (12)
- Displacement spool (15)
Distribution valve (12) consists of distribution valve internal block (16) and distribution valve external block (20) .
Cylinder block (11) contains pistons (14) and rollers (13) . These components work against cam ring (4) in order to generate torque. The displacement of all wheel drive piston motor (1) is controlled by displacement spool (15) . The charge oil acts against displacement spool (15) . Displacement spool (15) is a spring loaded valve. Displacement spool (15) is located in distribution valve internal block (16) .
The torque is generated by the pistons (14) of all wheel drive piston motor (1) . Each piston has a roller (13) . Each all wheel drive piston motor has ten pistons (14) . Each of the pistons are radially positioned in cylinder block (11) . Cam ring (4) has eight lobes. The cam is shaped similarly to a sine wave that is wrapped in a circle. High oil pressure from the pump works against the pistons, when the pistons are on the downward slope. When the cylinder block is fixed, torque is transmitted to the cam ring. This causes the cam ring to rotate. When the roller is at the bottom of the slope, the piston and the cylinder are blocked from the supply and return passages. When the roller moves beyond the bottom of the slope, the piston is connected to the return side of the loop and the oil is forced out of the cylinder as the roller moves up a slope on the cam. When the roller is at the top of the slope, the piston and the cylinder are blocked from the supply passages and the return passages. The piston and the cylinder will be blocked from the supply passages and from the return passages until the roller passes over the center and the cycle begins again.
Oil from cylinder block (11) fills motor housing (5) for the lubrication and the cooling.
Note: Due to the design of all wheel drive piston motor (1) , the forward direction is the most efficient direction. When all wheel drive piston motor (1) is in reverse at high speed, the efficiency drops.
Oil pressure enters distribution valve external block (20) through passages in spindle (2) . These passages send the oil to distribution valve internal block (16) . Oil from distribution valve internal block (16) passes into the cavity of piston (14) . The piston will push roller (13) against cam ring (4) . This is the initial start-up of all wheel drive piston motor (1) . Until the machine is running, the springs help to seat the distribution valve external block (20) against the face of the distribution valve internal block (16) . The oil pressure that is acting on the triangular design of the distribution valve internal block (16) seats the faces.
Large Displacement In The Forward Gear
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| Illustration 4 | g00275203 |
(15) Displacement spool (16) Distribution valve internal block (17) Level (18) Level (19) Level (20) Distribution valve external block (A) Port (B) Port (C) Passage (D) Passage (E) Passage (AA) Pump pressure oil (BB) Purge pressure oil | |
Oil that comes from the all wheel drive piston pump will enter the distribution valve internal block through port (A) . Also, the oil will enter distribution valve internal block (16) . Displacement spool (15) is not piloted. Distribution valve external block (20) is supplied power by level (17) and level (18) .
In level (17) , distribution valve external block (20) communicates with distribution valve internal block (16) by three passages (C) that are distributed at an angle.
In level (18) , distribution valve external block (20) communicates with distribution valve internal block (16) by three passages (D) that are distributed at an angle.
The oil return takes place through level (19) . The oil returns from distribution valve external block (20) through three passages (E) that are distributed at an angle. The oil enters distribution valve internal block (16) . Then, the oil flows outward through port (B) .
Large Displacement In The Reverse Gear
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| Illustration 5 | g00275204 |
(15) Displacement spool (16) Distribution valve internal block (17) Level (18) Level (19) Distribution valve external block (20) Port (A) Port (B) Passage (C) Passage (D) Passage (E) Passage (AA) Pump pressure oil (BB) Purge pressure oil | |
The oil that is coming from the all wheel drive piston pump enters the distribution valve internal block through port (B) . This oil feeds level (19) of distribution valve internal block (16) . Distribution valve external block (20) receives this oil through three passages (E) .
Level (17) and level (18) , which had been supplied with high pressure oil in the forward direction, are now fed with purge pressure. Level (17) and level (18) communicate with the return oil through passage (C) and passage (D) .
The reversal of the power supply will cause theall wheel drive piston motor to turn in the opposite direction.
Small Displacement In The Forward Gear
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| Illustration 6 | g00275205 |
(15) Displacement spool (16) Distribution valve internal block (17) Level (18) Level (19) Level (20) Distribution valve external block (A) Port (B) Port (C) Passage (D) Passage (E) Passage (Y) Port (AA) Pump pressure oil (BB) Purge pressure oil | |
The small displacement is obtained by piloting displacement spool (15) at port (Y) under low pressure. As a result, level (17) is isolated. Level (18) and level (19) intermittently communicate.
Hydraulic oil enters level (17) through port (A) . Then, the oil enters distribution valve internal block (16) . This allows three passages (C) in the distribution valve external block (20) to be fed with high pressure.
The purge pressure returns through level (18) and level (19) . Hydraulic oil from level (19) arrives in distribution valve external block (20) through three passages (E) . Also, the oil arrives at three passages (D) at level (18) . Then, the oil flows outward from port (B) toward the hydraulic oil tank.
Small Displacement In The Reverse Gear
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| Illustration 7 | g00275206 |
(15) Displacement spool (16) Distribution valve internal block (17) Level (18) Level (19) Level (20) Distribution valve external block (A) Port (B) Port (C) Passage (D) Passage (E) Passage (Y) Port (AA) Pump pressure oil (BB) Purge pressure oil | |
Level (17) becomes the return flow with the purge pressure. Three passages (C) are under purge pressure. Level (18) and level (19) are supplied with high pressure oil from three passages (D) and three passages (E) .
The reversal of the power supply will cause the all wheel drive piston motor to turn in the opposite direction.
Pistons and Cams
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| Illustration 8 | g00275208 |
Start-up of the all wheel drive piston motor (4) Cam ring (11) Cylinder block (13) Roller (14) Piston (16) Distribution valve internal block (AA) Purge pressure oil (FF) Return oil | |
The oil pressure enters distribution valve (20) through a passage. This passage sends the oil to distribution valve internal block (16) . Oil from the distribution valve internal block passes into the cavity of piston (14) . The piston pushes roller (13) against cam ring (4) . This is the initial start-up of the all wheel drive piston motor (1) .
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| Illustration 9 | g00275210 |
Full Force Phase (4) Cam ring (11) Cylinder block (13) Roller (14) Piston (16) Distribution valve internal block (AA) Purge pressure oil (FF) Return oil | |
The pressure which acts on piston (14) causes roller (13) to roll on the face of cam ring (4) . This will drive the cam ring in the direction that is shown by the arrow. Distribution valve external block (20) rotates in conjunction with cam ring (4) . This means that the supply passage moves from a partial connection to a full connection with the piston. This is the full force phase.
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| Illustration 10 | g00275213 |
Bottom Neutral Phase (4) Cam ring (11) Cylinder block (13) Roller (13A) Piston (14) Piston (16) Distribution valve internal block (AA) Purge pressure oil (FF) Return oil | |
When roller (13) goes to the bottom of cam ring (4) , the inlet port of piston (14) will be located between the valve passages. Since there is no connection with the passages, the piston does not drive on the face of the cam.
Piston (13A) takes over the function as the driving piston. This allows the roller of piston (14) to move up the face of the cam ring. Cam ring (4) and the distribution valve external block (20) will continue turning. Wheel spindle (1) , cylinder block (11) and distribution valve internal block (16) are stationary. This is the bottom neutral phase.
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| Illustration 11 | g00275214 |
Discharge Phase (4) Cam ring (11) Cylinder block (13) Roller (13A) Piston (14) Piston (16) Distribution valve internal block (AA) Purge pressure oil (FF) Return oil | |
When roller (13) of piston (14) moves up the face of the cam ring, the piston cavity is connected to the return line passage of distribution valve internal block (16) . This is the discharge phase.
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| Illustration 12 | g00275215 |
Top Neutral Phase (4) Cam ring (11) Cylinder block (13) Roller (13A) Piston (14) Piston (16) Distribution valve internal block (AA) Purge pressure oil (FF) Return oil | |
When roller (13) of piston (14) is at the top of cam ring (4) , the port of the piston will be located between two distributor passages. Since there is no connection between the two ports, piston (14) is neutralized. This position is the top neutral phase.
When roller (13) passes the top of the cam and starts to move down the opposite face, the piston cavity will connect with a new oil passage in distribution valve internal block (16) . This will give all wheel drive piston motor (1) a new start-up. Also, a new cycle will start for the piston.
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| Illustration 13 | g00275216 |
Start-up And Bottom Neutral Phase (4) Cam ring (11) Cylinder block (13) Roller (13A) Piston (14) Piston (16) Distribution valve internal block (AA) Purge pressure oil (FF) Return oil | |
The return passage between the piston cavity and distribution valve internal block (16) will gradually close as the roller moves upward on the cam ring. Piston (13A) is now at the bottom neutral phase.